424 



CREAM. 



TABLE CXLIX. 



SERIES I. 



The agreement is within the limits of experimental error. 



Instead of the formula given above, which includes a calcula- 

 tion of the percentage by volume of fat, the following approxi- 

 mate formula may be used 



V = 10 



where F is the percentage of fat by weight. For small differ- 

 ences the results by the two formulae agree sufficiently well. 



A practical method for the dilution of cream to constant 

 thickness may be founded upon the above formula. To take the 

 viscosity of a cream, a 10 c.c. pipette with a fairly wide opening, 

 marked with distinct lines both above and below the bulb, may 

 be employed ; it should be surrounded by a water-jacket made 

 of glass to ensure a constant temperature ; and the end should 

 not project far beyond the jacket. Care must be taken that its 

 position is always vertical during the test ; this may usually be 

 ensured by clamping the jacket firmly in position and fixing 

 the pipette by rubber corks. The position should be tested by 

 a plumb line, made of cotton, passing through the pipette. 



The " viscosity " of the cream is represented by the number of 

 seconds that the cream in the pipette takes to flow from the 

 mark above the bulb to that below, which can be determined 

 with sufficient accuracy by any watch with a seconds hand, 

 though it is preferable to use a stop watch. Care must be taken 

 that the cream is free from lumps, or solid particles, and it may 

 advantageously be filtered through muslin. The pipette should 

 be clean and dry, and the cream should be allowed to remain in 

 the pipette for a few minutes before making the test, in order to 

 ensure that its temperature is that of the jacket. 



It will be found in practice that it is better to use water of 

 the mean daily temperature in the jacket than water at any 



